The French patent application filed under No. FR 1262503 which describes a process for checking contact is for example known. In this case it is a matter of detecting changes in gradient reflecting the making of contact between the fastening component and the parts being assembled, any intermediate stage suggesting the possibility of prior play between the parts which are to be assembled, followed by tightening. It is then possible to consider whether, if the intermediate stage has not been detected, for example when the gradient of the tightening stage is correct, the parts are properly in contact; but if this intermediate stage is detected, it suggests play between the parts being assembled; assembly is then correct if the tightening gradient is consistent with expectations; if not a problem with contact has been detected.
Checking for the existence of these various stages makes it possible to be more sure that when the checked gradient is consistent with expectations it actually corresponds to proper tightening and is not an artefact associated with a problem in assembling the parts together.
In the context of threaded fasteners, such as for example a bolt, that is to say a bolt with a nut, it is also preferable to be able to ensure that tightening takes place on the properly formed threads of the bolt, that is to say away from those regions where the threads are incomplete or incorrectly formed which might occur at the two ends of the threaded portion of the shank of the bolt, and where there is no contact between the nut and a transitional portion of the bolt, that is to say the portion at the end of the thread, before the smooth part between the thread and the head of the bolt.
In addition to this it is advantageous to be able to carry out the check in real time, best avoiding additional action on the part of an operator.
At the present time the checking process comprises using wedges which enable the operator to check the geometrical parameters reflecting proper fastening. For this purpose the operator places a wedge in contact with the bolt, and if the geometric criteria corresponding to the specified conditions are complied with the wedge will not touch the parts which have to be checked. However if washers are used it can happen that they are of insufficient diameter for the operator to fit a wedge. This means that the assembly has to be dismantled so that the washer can be replaced, even if assembly was correct. In addition to this the operator generally needs to have on him a set of wedges corresponding to all the diameters which he has to tighten, often on the basis of different standards. In order to avoid one set of wedges for each standard it is possible to establish a general set of wedges, but this is less tolerant and therefore rejects a larger number of correct assemblies, which as a consequence results in more dismantling.